The disclosure of Japanese Patent Application No. HEI 2000-010836 filed on Jan. 19, 2000 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to a control system for a vehicle having a fuel cell, and an electric motor that is actuated by electric energy generated by the fuel cell.
2. Description of Related Art
Japanese Patent Laid-Open Publication No. SHO 50-31516 discloses a known type of vehicle which has a fuel cell and an electric motor for driving drive wheels of the vehicle through the use of electric energy generated by the fuel cell. In a four-wheel drive vehicle as disclosed in Japanese Patent Laid-Open Publication No. HEI 9-298803, an electric motor for driving drive wheels of the vehicle by use of electric energy generated by a fuel cell is used as at least one of a plurality of driving motors respectively provided for mutually independent front and rear wheel drive systems.
However, the above-mentioned publications disclosing the known vehicles provided with fuel cells do not disclose a technology for adequately controlling the drive systems, fuel cell, and others when one or more of the drive wheels slips, thus leaving a possibility for various improvements. For example, a vehicle using a fuel cell as an electric energy source for an electric motor may suffer from deterioration in the driving performance of the vehicle and the behavior of the vehicle when a drive wheel slips, for example, during four-wheel drive running, as compared with a conventional vehicle including an electric-energy storage device as an electric energy source for an electric motor. This problem may be caused by the properties of fuel cells, in particular, relatively low responsiveness.
The invention has been developed in the light of the above-described circumstances. It is therefore an object of the invention to provide a control system that controls a vehicle provided with a fuel cell so as to prevent the deterioration in the driving performance of the vehicle and the behavior of the vehicle at the time of slipping of a drive wheel, irrespective of the use of the fuel cell as an electric energy source for an electric motor.
To accomplish the above and other objects, the present invention provides a control system of a vehicle including a fuel cell and an electric motor that drives drive wheels of the vehicle with electric energy generated by the fuel cell, which control system comprises a traction controller that controls output of the drive wheels so as to secure tractive force of the vehicle when a predetermined traction control start condition is satisfied.
According to the invention as described above, even in the vehicle having a fuel cell, if any one of the drive wheels slips at the time of the start or acceleration, for example, on a low-xcexc road, the traction controller is able to restrict or control the output of the drive wheels, or the rotation of the drive wheels, so as to assure or improve the tractive force of the vehicle, while at the same time assuring improved transverse resistance and stability of the vehicle.
In one preferred form of the invention, the control system as described above may further include a fuel cell output controller configured to control output of the fuel cell during traction control by said traction controller. In this form of the invention, the output of the fuel cell is controlled by the fuel cell output controller during traction control of the traction controller, so that the fuel cell is appropriately operated in accordance with the traction control. For example, immediately after the start of the traction control, the electric motor is initially operated with electric energy supplied from an electric energy storage device, so as to generate assist torque. After a certain period of time, e.g., when the charge amount of the energy storage device falls short, the output of the fuel cell is controlled so that the electric motor is operated with electric energy supplied from the fuel cell. In this manner, the assist drive, or four-wheel drive, can be continued even if the traction control is performed for a prolonged time.
Preferably, the fuel cell output controller may reduce the output of the fuel cell so as to reduce the output of the electric motor during traction control by the traction controller, and, if the output of the electric motor is to be subsequently increased, an electric motor output controller may increase output torque of the electric motor by using electric energy from an electric energy storage device, thus assuring high acceleration response.
In another preferred form of the invention, the vehicle includes a first set of wheels and a second set of wheels, one of said first set and said second set comprising front wheels, the other of said first set and said second set comprising rear wheels, and wherein said first set of wheels are driven by an engine, and said second set of wheels are driven by the electric motor.
In the above form of the invention, the traction controller may reduce output of the engine that drives the first set of wheels so as to perform traction control, and an electric motor output controller may drive the electric motor using electric energy supplied from at least one of an electric energy storage device and the fuel cell, thus assuring improved responsiveness.
Preferably, the four-wheel drive vehicle further includes a generator that is driven by the engine, and the electric motor output controller drives the electric motor that drives the second set of wheels, using electric energy supplied from the generator, and drives the electric motor using electric energy supplied from the fuel cell when electric power generation of the generator is restricted, for example, due to heat generated by the generator. In this manner, the second set of wheels can be driven by the electric motor for a significantly increased period of time, with the electric motor being continuously operated.
In a further preferred form of the invention, the control system may further include a fuel distribution device that distributes fuel to the fuel cell and the engine. Preferably, the fuel distribution device reduces fuel to be supplied to the engine when an amount of fuel remaining in a fuel tank of the vehicle is equal to or less than a predetermined value. Thus, the operation of the engine having a relatively low efficiency is restricted when the remaining amount of the fuel is small, and the highly efficient fuel cell is used for driving the electric motor, thus assuring further improved fuel efficiency.
In another preferred form of the invention, the traction controller may operate to restrict output of the fuel cell when driving of the electric motor is controlled by the output of the fuel cell during traction control. Thus, heat generation of the fuel cell can be advantageously prevented during traction control. During the period of traction control in which the output of the fuel cell is restricted, electric energy is supplied from a generator driven by the engine to the electric motor, and therefore an assist operation by the electric motor is not restricted even if the output of the fuel cell is restricted. Furthermore, the driving force of the first set of wheels is reduced with the load on the engine being increased upon driving of the generator, thus assuring a further improved effect of traction control.
Preferably, the traction controller also performs traction control by operating wheel brakes that apply braking force to wheels of the vehicle. In this case, a high control response can be obtained in traction control by the traction controller.
In another preferred form of the invention, the control system further includes a correcting unit that corrects traction control by the traction controller, based on an operating condition of the fuel cell. In this case, the traction control that matches the power output state of the fuel cell can be performed. For example, as the magnitude of electric energy generated from the fuel cell to the electric motor, i.e., the assist torque generated by the electric motor, increases, reduction or restriction of the drive force (rotation) of the first set of wheels is relaxed, thus making it easy for the vehicle to run in a four-wheel drive mode.